Thin-film photovoltaics with functional components on the order of a few microns offer a path to realizing additive power on any surface of interest without excessive addition of weight and topography. To date, demonstrations of such ultra-thin photovoltaic cells have been limited to small-scale devices, often mounted on glass support substrates with only a few layers processed in solution.
MIT engineers have developed ultra-light fabric solar cells that can quickly and easily turn any surface into a power source. They developed these wafer-thin solar cells using scalable solution-based printing processes for all layers.
Attached to a tough, lightweight fabric, these resilient, flexible solar cells are much thinner than human hair, making them easy to mount on a permanent surface. They can be transported and quickly deployed to remote regions to assist in an emergency, or they can provide energy in flight as a portable power substance.
Unlike conventional solar panels, these new solar cells weigh less than 1 gram over the module surface (corresponding to an areal density of 105 gm−2). In addition, they generate 18 times more power per kilogram and are made from semi-conductive inks using printing processes that can be scaled up to large-area production.
Vladimir Bulović, the Fariborz Maseeh Chair in Emerging Technology, leader of the Organic and Nanostructured Electronics Laboratory (ONE Lab), director of MIT.nano, and senior author of a new paper describing the work, said: “The metrics used to evaluate a new solar cell technology are usually limited to their energy conversion efficiency and their cost in dollars per watt. Equally important is integrability: the ease with which the new technology can be adapted. The lightweight solar fabrics enable integration and give an impulse to current work. We aim to accelerate solar adoption given the current urgent need to deploy new carbon-free energy sources.”
Because conventional solar cells are so fragile, they must be covered with glass and packaged in a heavy, thick aluminum frame. This limits where and how they can be deployed.
In this new work, scientists are developing thin-film solar cells that are fully printable, using ink-based materials and scalable fabrication techniques. They use nanomaterials as printable electronic ink to make solar cells. In the cleanroom, they coated the solar cell structure with a slot-die coater. This deposits layers of the electronic materials onto a prepared, removable substrate that is only 3 microns thick. Later, they used screen printing to place an electrode on the structure to complete the solar module.
The printed module, about 15 microns thick, can then be peeled off the plastic substrate to create an ultra-light solar device.
However, such small, free-standing solar modules are difficult to implement because they rupture easily and are difficult to handle. The MIT team looked for a thin, flexible and strong substrate on which to mount the solar cells to overcome this difficulty. Fabrics were the best option because they provide mechanical resilience and flexibility with minimal added weight.
They discovered the perfect fabric: Dyneema, a composite fabric with a weight per square meter of only 13 grams. The fibers used to make this fabric are so powerful that they were used as ropes to lift the Costa Concordia, a sunken cruise ship, from the bottom of the Mediterranean Sea. They attach the solar panels to the plates of this cloth by applying a thin layer of UV-curing glue. This results in a fragile and durable mechanical solar structure.
Mayuran Saravanapavanantham, a graduate student in electrical engineering and computer science at MIT, said: “While it may seem simpler to print the solar cells directly onto the fabric, this would limit the selection of possible fabrics or other receiving surfaces to those that are chemically and thermally compatible with all the processing steps required to make the devices. Our approach decouples the production of solar cells from their final integration.”
In testing, the device was able to generate 730 watts per kilogram when freestanding and about 370 watts per kilogram when used on the high-strength Dyneema fabric, which is about 18 times more power per kilogram than conventional solar cells. They also tested the durability of their devices. They found that even after coiling and unrolling a solar panel more than 500 times, the cells still retained more than 90 percent of their initial power generation capacity.
Saravanapavanantham said: “A typical rooftop solar installation in Massachusetts is about 8,000 watts. To generate that same amount of power, our photovoltaics would only add 20 kilograms to the roof of a house.”
- Mayuran Saravanapavanantham, Jeremiah Mwaura, Vladimir Bulovic. Printed organic photovoltaic modules on transferable ultra-thin substrates as additive power sources. Small methods. DOI: 10.1002/smtd.202200940